This invention is directed generally to improvements in graphics display apparatus and specifically to cathode ray tube (CRT) display apparatus for displaying graphics in response to a viewer touching one or more selected areas on the CRT faceplate.
Conventional graphics display apparatus of the type under consideration include a CRT having a faceplate surrounded by a plurality of light sources and light detectors forming a network or grid of crossing light paths adjacent to the faceplate. Any interruption of a light path or beam, for example by a user touching the faceplate, results in a signal to a CRT graphics controller for changing the graphics displayed in accordance with the area touched and the system computer program. Thus the level of user skill and degree of user knowledge required for effective interaction with the computer are greatly reduced to an ability to read and touch. For obvious reaons these systems are very attractive and greatly enhance the marketability of computers.
A major problem in all such CRT display systems is that of assuring the integrity of each light beam in the grid, that is, to assure that any given light detector responds to light produced by its associated light source and not to light from other sources. There are many well-known schemes for accomplishing this result, all of which are generally referred to in this specification as rejection means. Rejection means have comprised light collimators or tubes to minimize the optical angle of the source, detector or both, elaborate electrical switching arrangements for simultaneously enabling a source and its associated detector and the use of expensive high speed, narrow band sources and detectors. The latter sources and detectors have even been used in switched systems to enhance system noise rejection.
The most commonly used interactive graphics display systems incorporate a form of computerized switching to sequentially energize a plurality of light sources disposed on adjacent sides of the faceplate. In some arrangements the corresponding light detectors, disposed across the faceplate from the sources, are also sequentially energized by the computer.
Needless to say, all such systems involve added complexity and expense to touch-operated graphics interactive display arrangements.